This rehabilitates language server support for Fuchsia.
This makes GnWorkspace more like PubWorkspace, not like BlazeWorkspace. The workspace is the location of `BUILD.gn` file (and is identical to the package, although I did not change this in this CL). And there must be also `.jiri_root` somewhere above it.
We don't look for `pubspec.yaml` files to decide that we have a new `ContextRoot`, instead we rely on `.dart_tool/package_config.json` created by `Pub` from `pubspec.yaml`. For GN, I had to specialize it to look for `BUILD.gn` files.
With this change `BUILD.gn` takes preference over any other signal, so we don't care if there are `pubspec.yaml` files.
Fixed: fuchsia:109640
Change-Id: I2277336bd377abb9d8c8c33529183e21b2f51c4e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/264280
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Konstantin Shcheglov
eea6fb106d